Melting safety devices of this type are already known and prevent undue pressure build-up in the gas system. For instance, in case of a fire, a material is selected for a blocking element, which material has a melting temperature in the range of up to about 220 degrees C. This material can be a tin alloy, such as is used commercially as a tin solder with a suitably low melting point. An opening for the discharge passage is located at a point which differs from the surrounding temperature. The gas can escape from the system through such discharge point. The discharge point is sealed by means of a soldered joint produced with the type of tin solder having a desirable melting point.
One disadvantage in this conventional melting safety device is that for the high operational pressures which will prevail, which pressures can be in the range of 500 bar or higher in pressure accumulators, critically high requirements must be satisfied in forming the solder connection. Since the solder connection will be continuously subjected to the operational pressure, the connection must be produced with great care and must be free of pores, in order to preclude any losses of pressure from the system. It is especially important that the solder diffuses somewhat, because it is continually under pressure.
With increasing temperatures, the rising pressure is generally outward, until the pressure opens the discharge passage. Another disadvantage of many known systems involves the difficulty in working with the melting safety device. For instance, to modify the control temperature, the entire gas system must be made pressureless with conventional safety devices.